Exclusive photoproduction of π⁰ up to large values of Mandelstam variables s, t and u with CLAS

M.C. Kunkel , 32 , 18 M.J. Amaryan , I.I. Strakovsky , 16 J. Ritman , 3 , 18 G.R. Goldstein , 43 K.P. Adhikari

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28 S Adhikari 13 H. Avakian 39 J. Ball 7 I. Balossino 19 L. Barion 19 M. Battaglieri 21 V. Batourine 39 27 I. Bedlinskiy 25 A.S. Biselli 11 5 S. Boiarinov 39 W.J. Briscoe 16 W.K. Brooks 40 39 S. Bueltmann 32 V.D. Burkert 39 F. Cao 9 D.S. Carman 39 A. Celentano 21 G. Charles 32 T. Chetry 31 G. Ciullo 19 12 L. Clark 42 P. L. Cole 17 M. Contalbrigo 19 O. Cortes 17 V. Crede 14 A. DAngelo 22 35 N. Dashyan 47 R. De Vita 21 E. De Sanctis 20 P.V. Degtyarenko 39 M. Defurne 7 A. Deur 39 C. Djalali 37 M. Dugger 2 R. Dupre 24 H. Egiyan 39 A. El Alaoui 40 L. El Fassi 28 L. Elouadrhiri 39 P. Eugenio 14 G. Fedotov 31 R. Fersch 8 46 A. Filippi 23 A. Fradi 24 G. Gavalian 29 Y. Ghandilyan 47 S. Ghosh 10 G.P. Gilfoyle 34 K.L. Giovanetti 26 F.X. Girod 39 D.I. Glazier 42 W. Gohn 9 E. Golovatch 36 R.W. Gothe 37 K.A. Griffioen 46 L. Guo 13 39 M. Guidal 24 K. Hafidi 1 H. Hakobyan 47 N. Harrison 39 M. Hattawy 1 K. Hicks 31 M. Holtrop 29 C.E. Hyde 32 D.G. Ireland 42 B.S. Ishkhanov 36 E.L. Isupov 36 D. Jenkins 44 K. Joo 9 M.L. Kabir 28 D. Keller 45 G. Khachatryan 47 M. Khachatryan 32 M. Khandaker 30 A. Kim 9 W. Kim 27 A. Klein 32 F. Klein 6 16 V. Kubarovsky 39 S.E. Kuhn 32 J.M. Laget 7 L. Lanza 35 P. Lenisa 19 D. Lersch 18 K. Livingston 42 I .J .D. MacGregor 42 N. Markov 9 G. Mbianda 32 B. McKinnon 42 T. Mineeva 9 V. Mokeev 36 R.A. Montgomery 42 A Movsisyan 19 C. Munoz Camacho 24 P. Nadel-Turonski 39 S. Niccolai 24 G. Niculescu 26 M. Osipenko 21 A.I. Ostrovidov 14 M. Paolone 38 K. Park 37 E. Pasyuk 39 D. Payette 32 W. Phelps 16 O. Pogorelko 25 J. Poudel 32 J.W. Price 4 S. Procureur 7 Y. Prok 45 D. Protopopescu 42 M. Ripani 21 B.G. Ritchie 2 A. Rizzo 35 G. Rosner 42 A. Roy 10 F. Sabatie 7 C. Salgado 30 S. Schadmand 18 R.A. Schumacher 5 Y.G. Sharabian 39 Iu. Skorodumina 37 36 D.G. Ireland 42 D. Sokhan 42 D.I. Sober 6 N. Sparveris 38 S. Strauch 16 M. Taiuti 21 15 J.A. Tan 27 M. Ungaro 33 H. Voskanyan 47 E. Voutier 24 D.P. Watts 41 L. Weinstein 32 X. Wei 39 D.P. Weygand 8 N. Zachariou 41 J. Zhang 45 Z.W. Zhao32 (The CLAS Collaboration)

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classification ✦ hep-ex hep-phnucl-exnucl-th

keywords crossdistributionenergygammalargemeasuredphotoproductionangular

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Exclusive photoproduction cross sections have been measured for the process $\gamma p \rightarrow p\pi^0(e^+e^-(\gamma))$ with the Dalitz decay final state using tagged photon energies in the range of $E_{\gamma} = 1.275-5.425$ GeV. The complete angular distribution of the final state $\pi^0$, for the entire photon energy range up to large values of $t$ and $u$, has been measured for the first time. The data obtained show that the cross section $d\sigma/dt$, at mid to large angles, decreases with energy as $s^{-6.89\pm 0.26} $. This is in agreement with the perturbative QCD quark counting rule prediction of $s^{-7} $. Paradoxically, the size of angular distribution of measured cross sections is greatly underestimated by the QCD based Generalized Parton Distribution mechanism at highest available invariant energy $s=11$ GeV$^2$. At the same time, the Regge exchange based models for $\pi^0$ photoproduction are more consistent with experimental data.

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Exclusive photoproduction of π⁰ up to large values of Mandelstam variables s, t and u with CLAS

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